Californian attackers armed with 5000 bullets, pipe bombs

Still from helicopter footage showing police going "door-to-door" searching for a potential third suspect involved in a shooting that killed 14 people and injured 17 more.

• Syed Rizwan Farook, Tashfeen Malik shot dead by police
• They gunned down 14 people at social centre
• Farook was 'devout' Muslim US citizen and had links to terror suspects
• Couple had dropped off their baby before killing spree

The two attackers who killed 14 people in a rampage at a banquet fired as many as 75 rifle rounds at the scene, left behind three rigged-together pipe bombs with a remote-control device that apparently malfunctioned, and had over 1600 more bullets with them when they were gunned down in their SUV, authorities said today.

At their home, they had 12 pipe bombs, tools for making more explosives, and over 3000 rounds of ammunition, Police Chief Jarrod Burguan said in a grim morning-after inventory that suggested yesterday's bloodbath could have been far worse.

Wearing military-style gear and wielding assault rifles, Syed Rizwan Farook, a 28-year-old county restaurant inspector, and his Pakistini wife, Tashfeen Malik, 27, slaughtered 14 and wounded 17 in the attack at a social service centre shortly after he slipped away from an employee banquet he was attending there.

The couple were shot to death about four hours later and a few kilometres away in a furious gunbattle with police.

As the FBI took over the investigation, authorities were trying to learn why the couple left behind their 6-month-old daughter and went on the rampage - the nation's deadliest mass shooting since the Newtown, Connecticut, school tragedy three years ago that left 26 children and adults dead.

"There was obviously a mission here. We know that. We do not know why. We don't know if this was the intended target or if there was something that triggered him to do this immediately," said David Bowdich, assistant director of the FBI's Los Angeles office.

At the White House, President Barack Obama said after meeting with his national security team that it was "possible this was terrorist-related" but that authorities were unsure. He raised the possibility that it was a workplace dispute or that mixed motives were at play.

Law enforcement experts said investigators may well conclude the killers had more than one motivation.

Farook was born in the US to a Pakistani family, was raised in Southern California and had been a San Bernardino County employee for five years, according to authorities and acquaintances. Authorities said Malik came to the US on a Pakistani passport in July 2014.

Police are slowly approaching a vehicle they believe contains at least one of the gunmen who attacked a disability centre

Police and federal agents for a second day searched a home in neighbouring Redlands, about 11km from the massacre at the Inland Regional Center. Investigators didn't immediately say if the couple had lived there. Public records show it may be the home of a Farook family member.

Sources have said Farook's apparent radicalisation contributed to his role in the mass shooting. Farook travelled to Saudi Arabia for several weeks in 2013 on the Hajj, the annual pilgrimage to Mecca that Muslims are required to take at least once in their lifetime.

This didn't raise red flags but it was during this trip that he met Malik, a native of Pakistan who came to the United States on a "fiancee visa" and later became a lawful permanent resident.

Officials had previously said that neither Farook nor Malik were known to the FBI but law enforcement officials said Farook had been in communication by phone and via social media with more than one person being investigated for terrorism, CCN reported.

Residents told KABC-TV Redlands is a sleepy town and expressed shock that the killers might be their neighbours.

The attackers invaded the centre at around 11am local time, opening fire in a conference area county health officials had rented for an employee banquet. Farook attended the banquet, then left and returned with murderous intent.

SBFD units responding to reports of 20 victim shooting incident in 1300 block of S. Waterman. SBPD is working to clear the scene.

Federal authorities said the two assault rifles and two handguns used in the violence had been bought legally, but they did not say how and when they got into the attackers' hands.

Co-worker Patrick Baccari said he was sitting at the same table as Farook, who suddenly disappeared. Baccari said that when the shooting started, he took refuge in a bathroom and suffered minor wounds from shrapnel slicing through the wall.

The shooting lasted about five minutes, he said, and when he looked in the mirror he realised he was bleeding. "If I hadn't been in the bathroom, I'd probably be laying dead on the floor," he said.

Baccari described Farook as reserved and said he showed no signs of unusual behaviour. Earlier this year, he travelled to Saudi Arabia, was gone for about a month and returned with a wife, later growing a beard, Baccari said.

The couple dropped off their daughter with relatives yesterday morning, saying they had a doctor's appointment, Hussam Ayloush, executive director of the Council on American-Islamic Relations, said after talking with family.

"We don't know the motives. Is it work, rage-related? Is it mental illness? Is it extreme ideology? At this point, it's really unknown to us, and at this point it's too soon to speculate," Ayloush said.

Co-workers told the Los Angeles Times that Farook was a devout Muslim but didn't talk about religion at work.

Farhan Khan, who is married to Farook's sister, told reporters that he last spoke to his brother-in-law about a week ago. Khan condemned the violence and said he had "absolutely no idea" why Farook would kill.

Seventeen people were wounded, according to authorities. As of last night, two patients were listed in critical condition.

About four hours after the late-morning carnage, police hunting for the killers riddled a black SUV with gunfire in a shootout 3km from the social services centre in this Southern California city of 214,000 people.

During the shootout, the couple fired 76 rounds, while law enforcement officers unleashed about 380, the police chief said.